Abstract
I-motif (IM) noncanonical DNA structures exist in cellular environments and are implicated in various diseases, including aging, cancer, and neurological disorders, making them attractive targets for drug development. IM DNA can act as molecular switches regulating transcription, especially within oncogenic promoter and telomere regions. This study investigates the interaction between kaempferol (KAE), a dietary flavonoid, with multiple IM DNA configurations alongside duplex DNA using extensive spectroscopic and thermodynamic approaches. UV-vis absorption studies show a 26.67% hyperchromic effect and a notable 15 nm red shift in the absorbance maxima of KAE upon HRAS1 IM binding. Fluorescence measurements indicate a 3.7-fold increase in emission intensity and a 17 nm red shift, coupled with an approximate 3 °C increase in melting temperature (T (m)), reflecting strong stabilization of HRAS1 IM by KAE. Our analyses also reveal that KAE preferentially binds HRAS1 IM with a binding constant (K (b)) of approximately 4 × 10(4) M(-1), significantly greater than that of duplex DNA (0.41 × 10(4) M(-1)). Time-resolved fluorescence decay and circular dichroism data support a predominant strong stacking mode of interaction. Thermodynamic parameters suggest that the binding process is spontaneous and enthalpy-driven. These findings demonstrate the potential of KAE to selectively target and stabilize HRAS1 IM DNA, suggesting a promising strategy for transcriptional regulation and anticancer drug design. Furthermore, KAE's pronounced excited-state intramolecular proton transfer fluorescence properties may serve as innovative tools for detecting and quantifying HRAS1 IM DNA in tumor cells, with potential applications in theranostics.